The Ileret area northeast of Lake Turkana
in northern Kenya occupies about 700 km². The area contains one of the most complete
stratigraphic sequences of the Koobi Fora Formation (Pliocene and Pleistocene),
and is renowned for its abundant mammalian fossils that include rare specimens
of hominids. Although the geology of the
Ileret area has been studied since 1969, published stratigraphic
information on the character of strata in this region is scant. Existing good descriptions of some parts of
the stratigraphy are in theses, which are not easily accessible to many
workers.
Strata in the area belong to the Omo Group composed of
Pliocene and Pleistocene deposits in the TurkanaBasin of southern Ethiopia and northern Kenya. Kenyan deposits
include the Nachukui Formation west of Lake Turkana,
and the Koobi Fora Formation east of the lake. The Shungura, Usno, Nkalabong, and Mursi Formations
are correlative deposits in the lower Omo Valley, Ethiopia. All eight members (Lonyumun,
Moiti, Lokochot, Tulu Bor, Burgi, KBS, Okote, and Chari)
are now identified in the Ileret area.
The area discussed is about twice as large as that covered
previously, and covers ~200 km2 not previously described. The composite thickness (513 m) of
section from the base of the Lonyumun Member to the top of the Chari Member is more than twice that reported by earlier
workers, but it compares well with the thickness of the composite section of
the Koobi Fora Formation. Several new tephra correlations between the Koobi Fora
Formation to the Nachukui Formation provide information on new time intervals
previously unknown in the Koobi Fora region.
The new stratigraphic column for the area enhances our understanding of
the geologic evolution of the Ileret area and the TurkanaBasin during the Pliocene and Pleistocene Epochs. In addition, the new stratigraphy provides a
very refined framework for fossils and artifacts collected within the area.
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